The invention pertains to methods of forming silicon nitride, and particularly pertains to methods of forming silicon nitride over silicon-oxide-comprising materials. The invention also pertains to methods of forming transistor devices, and further pertains to transistor device structures.
There are numerous semiconductor processing applications in which it is desired to form a silicon-nitride-comprising layer over a silicon-oxide-comprising layer. For instance, it can be desired to form transistor devices having silicon nitride and silicon oxide as dielectric materials between a conductive gate and a channel region. A difficulty in forming silicon nitride over silicon oxide is described with reference to FIGS. 1 and 2.
Referring initially to FIG. 1, a top view of a fragment of a semiconductor structure is shown. Fragment 10 comprises an oxide surface 12 upon which nitride 14 is to be formed. Oxide surface 12 can comprise, for example, silicon dioxide; and nitride 14 can comprise, for example, silicon nitride (Si3N4). The silicon nitride can be deposited by, for example, chemical vapor deposition. A problem is that the silicon nitride does not deposit readily on silicon dioxide, because there are only a few bonds available for bonding of nitrogen to silicon in silicon dioxide. Accordingly, the silicon nitride forms in small localized islands. The islands grow, and eventually merge to form a silicon nitride surface 14 that entirely covers silicon oxide 12. Such silicon nitride surface is shown in FIG. 2.
The silicon nitride material that ultimately forms the surface of FIG. 2 will typically be from about 30 to 35 xc3x85 thick, and will frequently be non-uniform in thickness as it was formed from the merger of relatively thick islands (frequently the islands are about 28 xc3x85 thick when they merge) so that the portions where edges of the islands merged are thinner than portions corresponding to centers of the islands. Further, it can be difficult to control the overall thickness of nitride material 14, as it is difficult to control how thick the islands of FIG. 1 will be when they finally merge.
It would be desirable to develop new methods of forming silicon nitride which overcome some or all of the above-discussed problems.
In one aspect, the invention encompasses a method of forming silicon nitride on a silicon-oxide-comprising material. The silicon-oxide-comprising material is exposed to activated nitrogen species from a nitrogen-containing plasma to introduce nitrogen into an upper portion of the material. The nitrogen is thermally annealed within the material to bond at least some of the nitrogen to silicon proximate the nitrogen. After the annealing, silicon nitride is chemical vapor deposited on the nitrogen-containing upper portion of the material.
In another aspect, the invention encompasses a method of forming a transistor device. A silicon-oxide-comprising layer is formed over a substrate. The silicon-oxide-comprising layer is exposed to activated nitrogen from a nitrogen-containing plasma to introduce nitrogen into an upper portion of the layer. The nitrogen is thermally annealed within the layer to bond at least some of the nitrogen to silicon proximate the nitrogen. After the annealing, silicon nitride is chemical vapor deposited on the nitrogen-containing upper portion of the layer. At least one conductive gate layer is formed over the silicon nitride, and defines a gate layer. A pair of source/drain regions are formed proximate the gate layer and gatedly connected to one another through a channel region that is beneath the gate layer.
In yet another aspect, the invention encompasses transistor device structures.